It is known to shape or deform high-strength and ultra high-strength steels in order to produce components from these steels. These shaping processes may, for example, include deep-drawing, stamping or roll-forming processes.
U.S. Pat. No. 7,197,824 B1 discloses a two-step system or stage to manufacture a bumper of “B” shape cross-section including a roll forming-welding stage where a straight cross member of a length to mount on the front or rear of various models of automobiles and the bending stage where any curvature or sweep is introduced into the cross member as required by the design of the automobile. The roll forming welding stage includes the spot or tack welding of the front wall to the web followed immediately by welding together without any gaps therebetween the abutting longitudinal edges utilizing a high frequency welder. Thus, the “B” shaped cross-section of the bumper may be used to make different bumpers of various lengths and curvatures.
The mechanical shaping of steel materials of this type leads to an increased occurrence of embrittlement phenomena, leading to crack formations in the material either immediately upon shaping or after a certain time.
These crack formations are explained by metallurgical inclusions of hydrogen from the environment in the material.
These inclusions are influenced to a very considerable extent by the local stress state in the material. The inclusion of hydrogen occurs to a very considerable extent in regions that are subject to tensile stresses. No or fewer inclusions are found in the region or regions that are subject to compressive stresses. This effect is very greatly magnified as the tensile strength of the material rises.
The effect is exacerbated still further by various sources of hydrogen which can preclude the use of a surface coating or can also lead to components of poor quality.
In standard processes used to produce components of this type, in particular in the automotive industry, for example during pressing, stamping and deep-drawing, very high tensile loads are involved in the production of the materials.
However, embrittlement and cracking of this type occurs not only in the regions that have been very strongly deformed, but also in the edge region, i.e. in the regions in which cutting or parting has taken place. This effect too is attributable to stress states and micro-cracking in the cut region.
However, this disadvantageous hydrogen embrittlement also occurs when high-strength and ultra high-strength steels of this type are welded. The effect of heat and correspondingly also of environmental elements or the atmosphere leads, in the region of the weld seam, to cracks attributable to hydrogen embrittlement. Despite these drawbacks, there is no substitute for these high-strength and ultra high-strength steels in the automotive industry, since reduced weight is nowadays a fundamental requirement of the automotive industry. Weight reduction of this type, however, can only be realized by using steels of considerably higher strength. However, one drawback is that the above-described hydrogen embrittlement and the properties of these steels mean that it is only possible to achieve certain degrees of deformation, which are lower than what would truly be desired. As a result, the shaping is subject to considerable restrictions and can only be achieved by large radii and short deep-drawing distances.
It is an object of the invention to provide a process for producing components from high-strength and ultra high-strength steels which can be used to achieve high degrees of deformation and to avoid embrittlement and cracking.
A further object of the invention is to provide a component made from a high-strength and ultra high-strength steel which has high degrees of deformation but in which no hydrogen embrittlement occurs.